Mold wash



United States Patent Ofilice Patented Dec. 10, 1963 3,113,360 MGLD WASH Paul 5. Neil, .l'r., Lansing, ill and Blames T. Baker, Mum star, End, assignors to Amsted Industries Incorporated, (lhlcago, lib, a corporation of New Jersey No Drawing. Filed Apr. 14, 1961, Ser. No. 102,927 11 (Ziairns. (Cl. 22-192) This invention relates generally to shell molds and more specifically to a novel mold wash which can be applied to the mold surface for the elimination of roughness and other surface defects in low carbon, low alloy steel castings as produced by shell molds.

As is well known in the art, shell molds are generally formed or" a mixture of silica or zircon sand and a thermosetting phenolic resin either in a powder form or in a solvent. Additionally, in some mixtures dust suppressants are employed for health purposes and in some instances a release agent is incorporated in the mixture to prevent the shell from adhering to the pattern which is heated during forming of the shell mold to set the resin.

lthough such shell molds ordinarily produce commercially acceptable iron castings and stainless steel castings, it is well known that low carbon, low alloy steel castings, such as those formed, for example, of grade B or C steel, are subject to characteristic surface defects when forme in such molds. Such surface defects are believed caused by a reaction between the molten steel and the mold, and between components of the mold. This reaction may be at least partially caused by the gases produced in the formation of silicon carbide by combination of carbon in the phenolic resin with the sand, and it is further believed that the molten steel may participate in this reaction by developing high temperatures sufficient to cause the production of such gas, and possibly the carbon in the steel accentuates the formation of such gas by participating in the reaction. It has also been discovered that the molten steel tends to pick up carbon from the mold when this reaction occurs resulting in undesirable carbon fluctuation in portions of the surface of the steel castings. This of course, adds to the surface roughness of the casting already attributable to the texture of the mold.

Various methods have been proposed in the past for overcoming the problems of such defects. For example, one method was the substitution of olivine, which is a relatively expensive magnesium silicate Within the range of forsteritc to fayalite. Such substitutes have, to a degree, improved the qualities or" low carbon, low alloy steel castings; however, the expenses of such substitutes has prevented commercial use of them.

Another approach has been the incorporation of ceramic powder into the shell mold mixture. After the shell mold is formed, the phenolic resin is burned out either by heating the entire mold or by burning the casting surfaces of the mold with a torch. Such expediencies have eliminated the characteristic surface defects of low carbon, low alloy steel castings produced in shell molds; however, in addition to the fact that the expense of such processes is prohibitive, it has also been found that they tend to destroy the dimensional accuracy or" the molds.

Still another approach has been the use of mold washes for preventing the steel from contacting the shell mold. One class of Washes in present commercial use employs metallic oxides. That is, the Wash may be comprised of one or more of the group of titanium dioxide, manganese dioxide and cerium dioxide particles in the form of a slurry of water and a suitable wetting agent. However, such washes have not proven to be entirely satisfactory.

Accordingly, the primary object of tion is to eliminate the characteristic tie present invensurface defects of low carbon, low alloy steel castings formed in conventional shell molds, without the necessity of altering the conventional shell mold mixture and without the necessity of burning the phenolic resin from the mold after formation thereof.

Another object of the invention is to wash the casting contacting surfaces of a conventional shell mold without destroying the dimensional accuracy thereof.

A still further object of the invention is to provide a novel wash for coating the castiru surfaces of a shell mold with a material which is preferably inert with respect to the molten steel and with respect to the phenolic resin and the sand in the presence of molten steel, to prevent the formation of gases or other phenomena causing the characteristic surface defect of low carbon. low alloy steel castings produced in conventional shell molds.

According to the present invention, it has been discovered that a solution comprised of, for example, stannous chloride or cupric chloride with. water and/ or alcohol is substantially completely effective for preventing the characteristic surface defects of low carbon, low alloy steel castings, when applied to the casting surfaces of a conventional shell mold.

After a conventional shell mold, comprised of sand and a thermo-setting resin, has been produced, in the usual manner, the casting contacting surfaces of the mold, which die-line the casting cavity in which the casting is to be formed by molten steel poured in the usual manner, are washed, as for example, by brushing or spraying a solu tion comprised of stannous chloride or cupric chloride with water and/ or alcohol. Such application of the wash to the casting surfaces can, of course, be made while the shell mold is still hot from the retention of heat absorbed during either the production of the mold or actual casting operations. Under such circumstances, the application of additional heat from external sources is not required since the retained heat of the shell mold is usually sufficient to complet y dry the wash on the casting surfaces. However, in some cases, as where the shell mold is already relatively cool, it may be necessary to dry the mold wash by the application or" additional heat. This may be accomplished, for example, by heating in an oven, by infra-red drying, or by application of a torch flame to the washed surfaces.

The shell mold is then filled with molten low carbon, low alloy steel herein defined as a steel having a carbon content not substantially in excess of about L5 percent by weight and content of chromium, manganese, nickel, molybdenum, copper, vanadium, titanium and alumium, severally or in any combination thereof within a rang of about nil to 15 percent by Weight. It has been found that steel castings produced in this manner are substantially free from the characteristic surface defects of low carbon, low alloy steel castings formed in shell molds according to conventional practices.

Several mold washes wh' b have been particularly efi ec tive for the purposes above described have been devised in accordance with the following formulations:

Wash N0. 1

89 parts by weight of water 20 parts by weight of ethyl alcohol parts by weight of stannous chloride Wash N0. 2

parts by weight of water 80 parts by weight of stannous chloride Wash N 0. 3

lGO parts by weight of ethyl alcohol 89 parts by weight of stannous chloride Wash N0. 4

80 parts by weight of water I 20 parts by Weight of ethyl alcohol 80 parts by weight of cupric chloride Wash N0.

100 parts by Weight of Water 80 parts by weight of cupric chloride Wash N0. 6

100 parts by weight of ethyl alcohol 80 parts by weight of cupric chloride it has also been found that the relative percentages of Water and alcohol may be varied in any desired relationship between the extremes illustrated by both Wash N0. 2 and Wash No. 3 or Wash No. 5 and Wash No. 6 depending on the composition of the particular shell molds to be coated. For example, if the particular shell mold has a waxy release agent on its surface or it the mold is of relatively low porosity, a higher concentration of alcohol is desirable since alcohol is a better wetting agent. Conversely, if the above conditions are relatively absent in the mold, a lower concentration of alcohol, or event a completely alcohol-free wash, is desirable because of cost factors.

In addition to the above washes it has been found that other metallic chlorides such as iron chloride, aluminum chloride or nickel chloride can be used instead of either stannous chloride or cupric chloride in achieving favorable results. Accordingly, in Washes NO; 1 through No. 6, the stannous chloride or cupric chloride can be replaced by an equivalent amount of either iron chloride, aluminum chloride or nickel chloride.

Further, it has been discovered that the relative percentage of either stannous chloride, cupric chloride, iron chloride, aluminum chloride, or nickel chloride, can be varied in accordance with, for example, the method of application. In accordance with this discovery, it has been found that in each of the Washes set out above, that is Wash No. 1 through Wash No. 6, the percentage of either of the metallic chlorides can be reduced to such a degree whereby the respective Wash is comprised of only 20 parts by weight of such metallic chloride instead of the 80 parts by Weight. The only difierence arising between such washes of either extreme is the time required to apply a suificient coating to the shell mold casting surfaces. Such a discovery is, of course, of extreme value Where the shell mold is designed for the casting of intricate and complex structures. That is, where the wash is to be applied as by spraying, it might be ditiicult to control the amount of coating applied to any particular area of the mold surface it the concentration of the metallic chloride is high. However, by reducing the concentration, the operator has a greater length of time in which to gauge the amount of coating applied.

The Wash may be applied to the casting surface of the mold cavity by any desired method such as brushing or spraying. The controlling factors for determining the amount of coating are, of course, the physical characteristics of the mold and the shape of casting to be produced.

We claim:

1. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then coating the mold cavity with a solution of stannous chlo ride, and then filling the mold cavity with molten steel.

2. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a therrno-setting resin, then coating the mold cavity with a solution of cupric chloride, and then filling the mold cavity with molten steel.

3. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then directly coating the surface of the mold cavity with a solution of metallic chloride, and then filling the mold cavity with molten steel.

4. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then coating the mold cavity with a solution of stannous chlo ride dissolved in a water-alcohol solvent, and then filling the mold cavity with molten steel.

5. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thcrmo-setting resin, then coating the mold cavity with a solution or" cupric chloride dissolved in a water-alcohol solvent, and then filling the mold cavity with molten steel.

6. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bondedtogether by a thenrno-setting resin, then coating the mold cavity with a solution of iron chloride, and then filling the mold cavity with molten steel.

7. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a therrno-setting resin, then coating the mold cavity with a solution of aluminum chloride, and then filling the mold cavity with molten steel.

8. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then coating the mold cavity with a solution of nickel chloride, and then filling the mold cavity with molten steel.

9. A method of producing low carbon, low alloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then coating the mold cavity with a solution of iron chloride dissolved in a water-alcohol solvent, and then filling the mold cavity with molt-en steel.

10. A method of producing low carbon, low mloy steel castings comprising: making a shell mold having sand particles bonded together by a thermo-setting resin, then coating the mold cavity with a solution of aluminum chloride dissolved in a water-alcohol solvent, and then filling the mold cavity with molten steel.

11. A method of producing low carbon, low alloy steel castings comprising: making a shell m'old having sand particles bonded together by a thermo-setting resin, then coating the mold cavity With a solution of nickel chloride dissolved in a water-alcohol solvent, and then filling the mold cavity with molten steel.

References Cited in the file of this patent UNITED STATES PATENTS 1,454,068 Myers May 8, 1923 1,802,946 Hoy Apr. 28, 1931 2,391,855 Bean Dec. 25, 1945 FOREIGN PATENTS 208,148 Australia May 1, 1957 

1. A METHOD OF PRODUCING LOW CARBON, LOW ALLOY STEEL CASTINGS COMPRISING: MAKING A SHELL MOLD HAVING SAND PARTICLES BONDED TOGETHER BY A THERMO-SETTING RESIN, THEN COATING THE MOLD CAVITY WITH A SOLUTION OF STANNOUS CHLORIDE, AND THEN FILLING THE MOLD CAVITY WITH MOLTEN STEEL. 